The present invention relates generally to the field of combustion dynamics. More specifically, the present invention relates to an acoustic impedance-matched fuel nozzle device, a tunable fuel injection resonator assembly, and associated methods suitable for use in conjunction with a gas turbine engine or the like.
It is known to those of ordinary skill in the art that relatively low-pressure drop fuel nozzles are important in the control of combustion dynamics in gas turbine engines and the like. Pressure fluctuations in a fuel nozzle may cause fuel flow rate fluctuations. Fuel flow rate fluctuations may interact with the flame of a combustor to produce pressure oscillations. The resulting fluctuation cycles may be either constructive or destructive, and may lead to oscillations with relatively large amplitude depending upon the magnitude and phase of the interactions. Thus, the acoustic characteristics of the fuel nozzle are critical in the control of gas turbine engine combustion dynamics.
A fuel line is characterized by an acoustic impedance (Z) to the propagation of an acoustic wave through it. This acoustic impedance may be expressed by the following equation:
Z=xcfx81 Co/A,xe2x80x83xe2x80x83(1)
where xcfx81 is the density, Co is the local speed of sound, and A is the cross-sectional area of the orifice used. The amount of acoustic energy reflected and transmitted are expressed by the power reflection coefficient, xcex1R=B2/A2, and the power transmission coefficient, xcex1T=1xe2x88x92xcex1R, where, in a given system, A is the amplitude of a downstream propagating wave and B is the amplitude of an upstream propagating wave. The orifice acoustic resistance is given by the incremental rate of change in the pressure drop with respect to the flow rate. An acoustic impedance matching condition arises when the acoustic impedance of the flow system is substantially equal to the orifice acoustic resistance. Given this condition, the acoustic impedance at the interface approaches untiy, maximizing the transfer of acoustic energy from the fuel nozzle to the combustor. For a fuel nozzle with internal acoustics that may be modified and/or controlled, or for active control schemes using an actuated valve, the resulting fuel pressure wave may be transmitted into the combustor with minimal attenuation. This is a critical step, enabling the internal acoustics of a fuel nozzle to interact acoustically with a combustor.
Conventional attempts at transmitting such a fuel pressure wave into the combustor without reflection have focused on using lumped-parameter soft nozzles or the like with orifices communicating to an internal fuel nozzle volume. Such an assembly is illustrated in FIG. 1. Referring to FIG. 1, it may be seen that a conventional two-stage fuel nozzle 10 includes an upstream orifice 12 and a downstream orifice 14. A captured response volume 16 is disposed there between. The upstream orifice 12 provides a relatively high pressure drop for the gaseous fuel to approximately the pressure of the compressor discharge air. The downstream orifice 14 provides a pressure drop comparable to the pressure drop across the openings of the combustor liner for the air supply. The dynamic pressure response characteristics of the fuel and air inlets to the premixer zone are substantially matched to eliminate variations in fuel/air concentration resulting from pressure variations in the premixer zone. The captured response volume 16 is sized sufficiently to store enough fuel to accommodate the mismatch in phase angle of fuel flowing into the captured response volume 16 through the upstream orifice 12 at a first phase angle relative to the phase angle of a pressure-forcing function in the premixer zone and fuel flowing out of the captured response volume 16 through the downstream orifice 16 at a second phase angle relative to the phase angle of the pressure-forcing function in the premixer zone. Although acoustic impedance matching is known to those of ordinary skill in the art in transmission line theory, what is still needed are systems and methods that apply it in the context of combustion dynamics.
In various embodiments of the present invention, a fuel nozzle device suitable for use in a gas turbine engine or the like is provided. The fuel nozzle device includes a fuel line and a plurality of gas orifices disposed at a downstream end of the fuel line, the plurality of gas orifices operable for injecting fuel into an air stream. The acoustic resistance of each of the plurality of gas orifices is chosen to match the acoustic impedance of the fuel line such that the maximum acoustic energy may be transferred between the fuel nozzle device and the combustor, thus enhancing the ability of the fuel nozzle device to control the combustion dynamics of the gas turbine engine system. The methods of the present invention may be applied to any combustion system incorporating a fuel injection system coupled to a combustion chamber or the like.
In various embodiments of the present invention, a fuel injection resonator assembly suitable for use in a gas turbine engine or the like is also provided. The fuel injection resonator assembly includes a plurality of orifices separated by a variable length tube. The area ratio of the plurality of orifices may be adjusted using, for example, an automated valve system to modify and/or control the relative flow resistance of the plurality of orifices. The resulting fuel injection resonator assembly acts as a tunable acoustic waveguide operable for delivering fuel to the combustor. The response of this tunable acoustic waveguide to external pressure perturbations may be modified and/or controlled.
In one embodiment of the present invention, a fuel nozzle device operable for injecting a fuel into an air stream and suitable for use in a gas turbine engine system or the like includes an orifice portion having a first cross-sectional area, Ah, and a first acoustic impedance, Z1, and a tube portion having a second cross-sectional area, AT, and a second acoustic impedance, Z2. The ratio of the first cross-sectional area, Ah, of the orifice portion and the second cross-sectional area, AT, of the tube portion is selected such that the first acoustic impedance, Z1, of the orifice portion is substantially the same as the second acoustic impedance, Z2, of the tube portion. When this occurs, the acoustic impedance at the orifice approaches unity and the power transmitted through the orifice is maximized (xcex1Txe2x86x921).
In another embodiment of the present invention, a method for controlling the combustion dynamics of a gas turbine engine system or the like includes providing an orifice portion having a first cross-sectional area, Ah, and a first acoustic impedance, Z1, and providing a tube portion having a second cross-sectional area, AT, and a second acoustic impedance, Z2. The method also includes selecting the ratio of the first cross-sectional area, Ah, of the orifice portion and the second cross-sectional area, AT, of the tube portion such that the first acoustic impedance, Z1, of the orifice portion is substantially the same as the second acoustic impedance, Z2, of the tube portion. Again, when this occurs, the acoustic impedance at the orifice approaches unity and the power transmitted through the orifice is maximized (xcex1Txe2x86x921).
In a further embodiment of the present invention, a fuel injection resonator assembly operable for injecting a fuel into an air stream and suitable for use in a gas turbine engine system or the like includes a tube portion operable for containing and transporting the fuel, wherein the tube portion comprises an upstream end and a downstream end, and wherein the length of the tube portion is adjustable. The fuel injection resonator assembly also includes a plurality of upstream orifices operable for delivering the fuel to the air stream, wherein the plurality of upstream orifices are disposed about the upstream end of the tube portion. The fuel injection resonator assembly further includes a plurality of downstream orifices operable for delivering the fuel to the air stream, wherein the plurality of downstream orifices are disposed about the downstream end of the tube portion. The length of the tube portion is selected to avoid or achieve assembly resonance in a predetermined range.
In a still further embodiment of the present invention, a fuel injection resonator assembly operable for injecting a fuel into an air stream and suitable for use in a gas turbine engine system or the like includes a tube portion operable for containing and transporting the fuel, wherein the tube portion comprises an upstream end and a downstream end, and wherein the length of the tube portion is adjustable. The fuel injection resonator assembly also includes a plurality of upstream orifices operable for delivering the fuel to the air stream, wherein the plurality of upstream orifices are disposed about the upstream end of the tube portion, and wherein the cross-sectional area of each of the plurality of upstream orifices is adjustable. The fuel injection resonator assembly further includes a plurality of downstream orifices operable for delivering the fuel to the air stream, wherein the plurality of downstream orifices are disposed about the downstream end of the tube portion. The length of the tube portion is selected to avoid or achieve assembly resonance in a predetermined range. The cross-sectional area of each of the plurality of upstream orifices is also selected to avoid or achieve assembly resonance in a predetermined range.
In a still further embodiment of the present invention, a method for controlling the combustion dynamics of a gas turbine engine system or the like includes providing a tube portion operable for containing and transporting a fuel, wherein the tube portion comprises an upstream end and a downstream end, and wherein the length of the tube portion is adjustable. The method also includes providing a plurality of upstream orifices operable for delivering the fuel to an air stream, wherein the plurality of upstream orifices are disposed about the upstream end of the tube portion, and wherein the cross-sectional area of each of the plurality of upstream orifices is adjustable. The method further includes providing a plurality of downstream orifices operable for delivering the fuel to the air stream, wherein the plurality of downstream orifices are disposed about the downstream end of the tube portion. The method still further includes selecting the length of the tube portion to avoid or achieve resonance of the tube portion, the plurality of upstream orifices, and the plurality of downstream orifices in a predetermined range. The method still further includes selecting the cross-sectional area of each of the plurality of upstream orifices to avoid or achieve resonance of the tube portion, the plurality of upstream orifices, and the plurality of downstream orifices in a predetermined range.